Matrix Metalloproteinase Expression Increases After Cerebral Focal Ischemia in Rats

Abstract

Background and Purpose-Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that degrade the extracellular matrix and are implicated in numerous pathological conditions including atherosclerosis, inflammation, and tumor growth and metastasis. In the brain, the endothelial cell wall, strengthened by tight junctions, defines the blood-brain barrier (BBB). The extracellular matrix molecules constitute the basement membrane underlying the vasculature and play a critical role in maintaining the integrity of the BBB. After focal stroke, there is a breakdown of the BBB with an associated increase in vascular permeability, inflammatory cell influx, and neuronal cell death. The present study was designed to investigate the effects of MMP expression after stroke. Methods-Focal stroke was produced by permanent middle cerebral artery occlusion (MCAO) in the rat, and MMP protein expression was measured by Western blot and zymogram analysis over a time course ranging from 6 hours to 30 days (nϭ32). Immunohistochemistry at 1 and 5 days (nϭ8 and 6, respectively) was also utilized to characterize the expression of several MMPs and related proteins after stroke, including their cellular source. To test the hypothesis that early increased MMP-9 expression is involved in ischemic brain injury, a neutralizing monoclonal antibody directed against MMP-9 was administered intravenously (nϭ7 per group) 1 hour before MCAO, and infarct size was measured 24 hours later. Results-MMP expression increased progressively over time after stroke. After 12 hours, significant (PϽ0.05) MMP-9 activity was observed that reached maximum levels by 24 hours (PϽ0.001), then persisted for 5 days at this level and returned to basal (zero) levels by 15 days. On the basis of morphological criteria, MMP-9 appeared to stain with endothelial cells and neutrophils identified both within and at the periphery of the infarct within 24 hours of focal ischemia. After 5 days, MMP-9 appeared to stain with macrophages present within the infarcted brain. MMP-2 activity was significantly (PϽ0.001) increased by 24 hours and was maximum after 5 days following MCAO. MMP-2 appeared to stain with macrophages present within the infarcted region. Unlike MMP-9 and MMP-2, tissue inhibitor of metalloproteinase-1 was identified at comparable levels in both control and ischemic tissue after MCAO. MMP-1 and MMP-3 could not be detected in the brain after focal stroke. When an MMP-9 -neutralizing monoclonal antibody was administered systemically, animals exhibited significantly reduced infarct size (ie, a 30% reduction compared with non-immune antibody controls; PϽ0.05). Conclusions-These results demonstrate that early increased MMP-9 expression in endothelial cells and infiltrating neutrophils is a significant response to cerebral focal ischemia and that selective inhibition of MMP-9 activity can significantly reduce brain injury after stroke.

Matrix Metalloproteinase-Mediated Disruption of Tight Junction Proteins in Cerebral Vessels is Reversed by Synthetic Matrix Metalloproteinase Inhibitor in Focal Ischemia in Rat

“…There was expression of MMP-9 mRNA, but not that of MMP-2, which was consistent with the protein expression. Earlier studies had demonstrated expression of MMP-9 at 24 h (Rosenberg et al, 1996;Romanic et al, 1998;Gasche et al, 1999). A striking feature of the later injury to the BBB was the appearance of the TJPs in the astrocytes.…”

Matrix metalloproteinases in neuroinflammation

“…The presence of MMP-2-containing astrocytic foot processes near the fluid-controlling surfaces of the brain suggests a role for MMP-2 in the normal fluid balance in the brain or in the regulation of the BBB. In a rat model of permanent ischemia, MMP-9 was identified in cerebral blood vessels and in inflammatory cells (Romanic et al, 1998). The MMPs have been studied in temporary ischemia caused by 90-min occlusion of the middle cerebral artery by a suture thread with reperfusion for various times (Rosenberg et al, 2001a).…”

Matrix Metalloproteinase-9 Undergoes Expression and Activation during Dendritic Remodeling in Adult Hippocampus

“…Considering that past results have been inconsistent with respect to the cellular localization of MMPs in the brain (Del-Bigio and Jacque, 1995;Backstrom et al, 1996;Gottschall and Deb, 1996;Lim et al, 1996;Romanic et al, 1998), we first investigated the tissue distribution of MMPs within the rat forebrain by means of in situ hybridization and immunocytochemistry. Coronal sections of 2-month old rat brains were analyzed at the level of the dorsal hippocampus (Fig.…”